Poly(arylene sulfide) sheet and production process thereof

ABSTRACT

A poly(arylene sulfide) sheet excellent in planarity and smoothness is formed of a poly(arylene sulfide) having a melt viscosity, η* of 1,000-25,000 poises as measured at 310° C. and a shear rate of 200 sec -1 , and a melt crystallization temperature, Tc 2  or 170°-240° C., wherein Tc 2  is an exothermic peak temperature of crystallization which appears upon the measurement by a differential scanning calorimeter at a cooling rate of 10° C./min after the polymer is heated from 23° C. to 380° C. at a rate of 10° C./min and then held for 3 minutes at 380° C. It has a surface roughness, Ra of 0.09 μm or less on at least one side thereof and a degree of crystallization of at least 5%. Its number of flexings to break, Y satisfies the following equation (I): 
     
         log Y≧7.11-2.34log t                                (I) 
    
     wherein t means a thickness (μm) of the sheet. The sheet is produced by melt-extruding the poly(arylene sulfide) through a slit die into a sheet-like form and then cooling and crystallizing the sheet on a casting roll. The temperature, T (°C.) of the casting roll is controlled to a temperature in a range satisfying the following equation (II): 
     
         120≦T≦190-0.02t                              (II) 
    
     wherein t means a thickness (μm) of the sheet, thereby conducting the cooling and the crystallization of the sheet at one stage.

FIELD OF THE INVENTION

This invention relates to a sheet of a poly-(arylene sulfide) which mayhereinafter be called "PAS", and more specifically to a PAS sheetcomposed of a PAS and having excellent dimensional stability to heat,planarity, smoothness and mechanical properties such as flex resistanceand to a production process thereof.

BACKGROUND OF THE INVENTION

Films composed principally of a PAS typified by poly(phenylene sulfide)which may hereinafter be called "PPS" have excellent properties such ashigh heat resistance, chemical resistance and mechanical strength, andgood electrical properties and are useful for various industrialapplications.

Stretched PAS films however involve a problem that they tend to undergodeformations such as heat shrinkage in a high temperature range.Unstretched PAS sheets of smaller orientation are hence used forapplications where high-temperature dimensional stability is required.In this case, since PAS has a lower glass transition temperature, itscrystallization is indispensable in order to impart heat resistance tothe sheets. The reason is that among conventional unstretched PASsheets, uncrystallized ones show significantly lowered strength when thetemperature increases to 100° C. or so and they hence undergo greatdeformation under a slight load. As illustrated in FIG. 1 by way ofexample, when the unstretched sheets are heated up at a constant rateunder a slight fixed load, an uncrystallized sheet shows a highelongation from about 120° C. as depicted by a line (3), indicating thatit is deformed to a great extent by the slight load. On the other hand,a sheet having a degree of crystallization of 6% does not exhibit such agreat deformation at about 120° C. as the uncrystallized sheet has shownas depicted by a line (1). Further, it is found that a sheetcrystallized to a degree of crystallization sufficiently as high as 24%shows a little deformation at high temperatures as depicted by a line(2) and its high-temperature dimensional stability is hence good.Unstretched PAS sheets sufficiently crystallized by conventionalcrystallization processes are however accompanied by disadvantages thatthey have a low elongation and are liable to be brittle.

With respect to the improvements of unstretched PPS sheets, variousproposals have been made in, for example, Japanese Patent PublicationNo. 42611/1984, and Japanese Patent Application Laid-Open Nos.121052/1982, 184619/1984 and 251121/1987 to date.

Conventionally, crystallization of an unstretched PAS film has beeneffected by subjecting an amorphous sheet to a heat treatment in atemperature range of from the glass transition point of PAS or higher toits melting points or lower. Namely, a sheet-like formed productcomposed principally of PPS has generally been produced by melting thestarting resin, extruding the melt through a slit die, cooling andsolidifying the extrudate into an amorphous sheet, and then subjectingthe sheet to a heat treatment.

The conventional heat treatments for crystallization include, forexample, a method in which a sheet to be treated is brought into contactwith a heated liquid or gas stream or a surface of a heated solid suchas a roll (Japanese patent publication No. 42611/1984). It has also beenknown to smoothen the surface of a sheet-like material by subjecting thesheet-like material to a heat treatment while supporting it with clampsor the like at its periphery or causing it to continuously pass througha hot-air oven in a state supported at one or two points continuously orheat treating it on a smooth stainless steel belt, followed bycompression forming or pressing between pressure rolls (Japanese patentApplication Laid-Open No. 184619/1984).

These conventional heat treatment methods are however difficult toprovide sheets excellent in both planarity and smoothness whenunstretched pAB sheets are industrially produced. Moreover, theprovision of a smooth PAS sheet requires a complex step such ascompression forming or rolling, so that larger production facilities arerequired.

Incidentally, the behavior of a PAS sheet upon its heat treatmentincludes that a sheet cooled and solidified in an amorphous state isexposed to a temperature above the glass transition point owing to itsheating and upon a lapse of a predetermined time, is crystallized andhardened. When a PAS sheet is subjected to a heat treatment in a heatedliquid or gas stream by way of example, the sheet expands and becomessticky as the temperature increases. When the temperature increasesbeyond the glass transition point of the PAS and the sheet becomes soft,the sheet is distorted or locally elongated, sticks to another materialor object which is in contact with the sheet, or forms a roughenedsurface due to eruption of low boiling materials contained inside thePAS. Crystallization thereafter proceeds, and the sheet shrinksvolumetrically by its density increment accompanied by thecrystallization and hence undergoes changes in dimension correspondingto the volumetric shrinkage, thereby hardening the sheet. The resultantsheet is however poor in planarity and its surface conditions areinferior.

In addition, in the crystallization owing to heated air, a PAS becomesvery soft at its glass transition point or higher and a PAS sheetdeforms and/or breaks due to a slight wind pressure. Indeed, it is henceextremely difficult to obtain a sheet excellent in smoothness. Further,the growth of spherulites is also remarkable. It is hence only possibleto obtain a sheet inferior also in planarity.

As described above, the PAS sheet expands with heat and becomes soft inthe course of the heat treatment. Therefore, unless the sheet ismechanically fixed during the heat treatment, the planarity of the sheetis reduced and thickness irregularity occurs, thereby deteriorating itsappearance.

In the heat treatment method in which a PAS sheet is simply brought intocontact with a surface of a solid such as a heating roll or stainlesssteel belt, the sheet expands and moreover becomes sticky as thetemperature increases and at the same time, volumetric shrinkage causedby crystallization occurs. Accordingly, the sheet may locally andslightly float from the surface of the solid. In addition, entrainmentof air is also observed. Subsequent crystallization results in hardeningof the sheet. In this case, height differences arise in the surface ofthe sheet between areas maintained in contact with the solid and thosefloated from the solid. It is hence only possible to obtain a sheetinferior in planarity.

When a PAS sheet is subjected to a heat treatment by means of a tenterwhile holding it with clips or the like, the clipped parts becomeuseless and moreover, the resultant sheet is susceptible to breakagefrom the clipped parts. Besides, the tenter involves an economicalproblem because its equipment cost and operating cost are expensive.

Even if such a crystallized PAS sheet of poor planarity is pressed bycompression forming or rolling, it is impossible to fully remove thethickness irregularity, warpage, small ruggedness and the like to makethe sheet excellent in planarity and smoothness because it has alreadybeen crystallized. Moreover, the process is complex and there is hence adisadvantage also from economical consideration.

The present inventors previously found that a PAS sheet excellent inplanarity and smoothness can be obtained by upon heat treatment of anamorphous PAS sheet through a heating roll, preheating the sheet andthen causing the thus-preheated sheet to pass between the heating rolland a pinch roll under a pinch pressure of 0.05-10 kg/cm, whereby thesheet is continuously pressed under linear pressure, and applied for apatent (Japanese Patent Application No. 329542/1987). As has beendescribed therein, when the PAS sheet is crystallized on the heatingroll while controlling temperature and contact pressure by making use ofthe pinch roll, its planarity can be improved to a great extent comparedto conventional sheets, there are however potential problems that theruggedness on surface of the pinch roll is transferred on the surface ofthe sheet and/or coarse spherulites generate. Therefore, this process isstill insufficient to use in fields where high planarity and smoothnessare required. In addition, a separate step for conducting the heattreatment is required in this process.

It has been proposed to in the production of a crystallized polyetherether ketone film, conduct cooling and crystallization of a film at onestage by controlling the temperature of a casting roll to a temperaturein a range of 150°-250° C. (Japanese Patent Application Laid-Open No.92430/1988). When this process is applied to the production process of asheet making use of a conventional PAS low in melt crystallizationtemperature, Tc₂, crystallization of the sheet on the casting roll isinsufficient, and moreover since the PAS is characterized by highsusceptibility to elongation when it is in the amorphous state at atemperature not lower than its glass transition point, the sheet adheresclosely to the roll and hence becomes poor in separation property fromthe roll. It is hence only possible to obtain a sheet inferior inplanarity, smoothness and physical properties.

Moreover, when the PAS is used, there is a potential case where aresulting sheet may have low flexing properties even if the sheet isgood in appearance. It is hence necessary to select suitably thetemperature and time ranges of the process.

OBJECT AND SUMMARY OF THE INVENTION

An object of this invention is to provide a PAS sheet excellent indimensional stability to heat, planarity, smoothness, flex resistance,etc.

Another object of this invention is to provide a PAS sheet excellent inphysical properties, particularly, planarity of the sheet surfaces by aneconomical process.

A further object of this invention is to provide a PAS sheet havingexcellent dimensional stability to heat, planarity, smoothness, flexresistance, etc. and containing solvent-extracted low-molecular weightmaterials such as oligomers in smaller amounts.

The present inventors have carried out an extensive investigation with aview toward solving the above-mentioned drawbacks of the prior art. As aresult, it has been found that a PAS sheet excellent in planarity, highin smoothness on at least one side of the sheet and superb in mechanicalproperties such as flex resistance can be economically obtained bymelt-extruding a high molecular weight PAS having a high meltcrystallization temperature range through a slit die into a sheet-likeform and then cooling and crystallizing the sheet at one stage on acasting roll controlled within a specific temperature range.

In addition, it has also been found that when a PAS having a highmolecular weight and a high melt crystallization temperature range andtreated in advance by melt-extruding by a vented extruder while drawinga vacuum from a vent zone through a vent port is used as the above PAS,a PAS sheet in which materials extracted by extraction with xylene isreduced to 0.5 wt. % or less of the whole weight before extraction andwhich hence contains solvent-extracted low-molecular weight materialssuch as oligomers in smaller amounts can be obtained. The PAS sheetcontaining solvent-extracted low-molecular weight materials in smalleramounts is suitable for use as a sheet for insulating the motors ofcoolant-compressors.

These findings leads to completion of the present invention.

In an aspect of this invention, there is thus provided a poly(arylenesulfide) sheet excellent in planarity and smoothness. The sheet isformed of a poly(arylene sulfide) having a melt viscosity, η^(*) of1,000-25,000 poises as measured at 310° C. and a shear rate of 200sec⁻¹, and a melt crystallization temperature, Tc₂ of 170°-240° C.,wherein Tc₂ is an exothermic peak temperature of crystallization whichappears upon the measurement by a differential scanning calorimeter at acooling rate of 10° C./min after the PAS is heated from 23° C. to 380°C. at a rate of 10° C./min and then held for 3 minutes at 380° C. Thesheet features that:

(a) the surface roughness, Ra of at least one side of the sheet is 0.09μm or less;

(b) the degree of crystallization of the sheet is at least 5%; and

(c) the number of flexings to break, Y of the sheet satisfies thefollowing equation (I):

    log Y≧7.11-2.34log t                                (I)

wherein t means a thickness (μm) of the sheet.

In another aspect of this invention, there is also provided a processfor the production of a poly(arylene sulfide) sheet excellent inplanarity and smoothness. The process comprises melt-extruding apoly(arylene sulfide) through a slit die into a sheet like form and thencooling and crystallizing the sheet on a casting roll. The process ischaracterized in that the above-described poly(arylene sulfide) is usedas a poly(arylene sulfide), the temperature, T (° C.) of the castingroll is controlled to a temperature in a range satisfying the followingequation (II):

    120≦T≦190-0.02t                              (II)

wherein t means a thickness (μm) of the sheet, thereby conducting thecooling and the crystallization of the sheet at one stage.

Compared with the crystallized PAS sheets obtained in accordance withthe conventional processes by subjecting a quenched and soldifiedamorphous sheet to a heat treatment, the PAS sheets according to thisinvention are excellent in planarity, extremely smooth on at least onside of the sheet surfaces and also superb in mechanical properties suchas flex resistance.

Moreover, according to this invention, it is possible to provide a PASsheet having an excellent planarity, smoothness and flex resistance andcontaining materials extracted by extraction with xylene in an amount of0.5 wt. % or less of the whole weight before extraction by using, as thePAS, a PAS obtained by melt-extruding by a vented extruder in advancewhile drawing a vacuum from a vent zone through a vent port.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 diagrammatically shows the elongation or shrinkage behaviordepending on heating temperatures of each sheet obtained in Example 14,and is a graph obtained by measuring the sheet by a "Thermo MechanicalAnalyzer (TMA) 40" manufactured by Mettler Instrument AG while heatingit at a heating rate of 2° C./min under a minimum load of 1.7 g/mm²,wherein lines (1), (2) and (3) correspond to Sheet A (degree ofcrystallization: 6%), Sheet B (degree of crystallization: 24%) and SheetC (degree of crystallization: 0%) in Example 14, respectively:

FIG. 2 diagrammatically shows a relationship between the temperature ofa casting roll and the degree of crystallization of a poly(p-phenylenesulfide) sheet upon the production of sheets of 200 μm thick, wherein Aand B indicate a case where the residence time on the casting roll is 90seconds and a case where the residence time on the casting roll is 50seconds, respectively;

FIG. 3 diagrammatically shows a relationship between the temperature ofa casting roll and the degree of crystallization of a poly(p-phenylenesulfide) sheet upon the production of sheets by controlling theresidence time to 90 seconds, wherein C and D indicate a sheet of 400 μmthick and a sheet of 200 μm thick, respectively; and

FIG. 4 diagrammatically shows a relationship between the degree ofcrystallization and the flex resistance (in terms of the number offlexings to break) for poly(p-phenylene sulfide) sheets having aspecific thickness, wherein ○ and ○ indicate sheets of 200 μm thick,which have been produced by using poly(p-phenylene sulfides) having meltviscosities, η^(*) of 6,000 poises and 2,600 poises, respectively.

DETAILED DESCRIPTION OF THE INVENTION PAS

In this invention, PAS is used as a raw material of a sheet. The term"PAS" as used herein means PAS alone and resin compositions comprising,as a principal component, PAS and incorporated with one or more otherthermoplastic resins, fillers, antioxidants, nucleating agents and/orother additives therein. (PAS)

In order to permit formation into a sheet, the PAS useful in thepractice of this invention should be a substantially linear,high-molecular weight PAS whose melt viscosity, η^(*) is 1,000-25,000poises, preferably, 3,000-20,000 poises as measured at 310° C. and ashear rate of 200 sec⁻¹.

The term "substantially linear, high-molecular weight PAS" as usedherein means a polymer obtained from a monomer composed principally of asubstantially bifunctional monomer. Incidentally, the PAS may be apolymer in which a partially branched structure has been introduced, forexample, by causing a small amount of a polyhalogenated benzene to existas a monomer.

If the melt viscosity of the PAS is lower than 1,000 poises, the PAS isinferior in film-forming property and is unable to provide a sheetstably, and moreover a resulting sheet becomes low in flexing property.On the contrary, any melt viscosities exceeding 25,000 poises make itdifficult to melt-extrude the PAS stably.

The PAS employed in this invention should be a PAS whose meltcrystallization temperature, Tc₂ is 170°-240° C., preferably, 180°-240°C., more preferably, 200°-240° C., wherein Tc₂ is an exothermic peaktemperature of crystallization which appears upon the determination by adifferential scanning calorimeter (hereinafter abbreviated as "DSC") ata cooling rate of 10° C./min after the PAS is heated from 23° C. to 380°C. at a rate of 10° C./min and then held for 3 minutes at 380° C.

If Tc₂ is lower than 170° C., the crystallizing rate on a casting rollof the sheet melt-extruded becomes slow and its crystallization hencerequires a lot of time, so that the PAS is unsuitable for practical use.In addition, since the crystallization on the casting roll isinsufficient, the sheet closely adheres to the surface of the roll andhence is hard to come away from the roll. Therefore, trouble such aslocal elongation of the sheet arises. It is hence only possible toobtain a sheet inferior in planarity, smoothness and appearance and poorin mechanical properties. If Tc₂ is higher than 240° C. on the contrary,the crystallization speed of the PAS sheet is too fast, so that it isdifficult to obtain a sheet having sufficient flexing resistance. Thisis believed to be attributed to the fact that the crystalline structurein the thickness-wise direction of the PAS sheet becomes uneven.

Such a substantially linear, high-molecular weight PAS can be obtainedsuitably by subjecting an alkali metal sulfide and a dihalogenatedaromatic compound to specific two-stage heat-up polymerization in thepresence of water in an organic amide solvent such asN-methylpyrrolidone as disclosed in Japanese Patent ApplicationLaid-Open No. 7332/1986.

Illustrative examples of the alkali metal sulfide may include lithiumsulfide, sodium sulfide, potassium sulfide, rubidium sulfide, cesiumsulfide, and mixtures thereof.

As exemplary dihalogenated aromatic compounds, may be mentionedp-dichlorobenzene, m-dichlorobenzene, 2,5-dichlorotoluene,p-dibromobenzene, 2,6-dichloronaphthalene,1-methoxy-2,5-dichlorobenzene, 4,4'-dichlorobiphenyl,3,5-dichlorobenzoicacid, p,p'-dichlorodiphenyl sulfone, 4,4'-dichlorodiphenyl sulfoxide,4,4'-dichlorodiphenyl ketone, and mixtures thereof.

PAS useful in the practice of this invention are substantially linear.Of these, poly(phenylene sulfide), particularly, poly(p-phenylenesulfide) or poly(p-phenylene sulfide) copolymers containing m-phenylenesulfide units as a minor component are preferred. In addition,poly(p-phenylene sulfide) copolymers in which a partially branchedstructure is introduced by copolymerizing a polyhalogenated benzene as aminor component may be used suitably.

Optional components

Although a PAS alone may be used in this invention, it is also feasibleto add a small amount of a polyolefin such as polyethylene,polypropylene or poly-4-methyl-pentene-1, a rubber such as polyisoprene,or a thermoplastic resin such as polyethylene terephthalate,polycarbonate, tetrafluorinated ethylene resin, polyether ether ketone,poly(ketone sulfide), polyamide, aromatic polyimide, aromatic polyester,polystyrene, polyacrylic acid ester, polymethacrylic acid ester,polyether nitrile, polyether ketone, polyether ketone ketone,polysulfone or polyetherimide.

It is also feasible to incorporate one or more of various organic andinorganic fillers such as glass fibers, aromatic polyamide fibers,carbon black, talc, clay, titanium oxide, molybdenum disulfide andcarbon fibers.

Besides, additives such as antioxidant, heat stabilizer and lubricantmay also be incorporated.

Among various additives, carbon black, silicon oxide, kaolin, clay,titanium oxide or the like is preferably added as a nucleating agent inparticular. Such addition restrains the growth of spherulites in acrystallized sheet and hence makes surfaces of the sheet more smooth.When a melt-extruded sheet is pinned on a casting roll while applyingstatic electricity, coarse spherulites tend to form on the pinnedsurface. However, the addition of the nucleating agent effectivelyrestrains such formation.

Besides, the addition of a laminal or fibrous inorganic filler such asmica or carbon fibers is effective in the improvement of the stiffnessof the sheet.

These optional components may be mixed by a conventional mixing method,or may be mixed in a molten state and pelletized and thereafter fed to amelt extruder.

Production Process of PAS Sheet

Upon formation of a PAS sheet, a PAS is generally fed to a melt extruderand then heated to a temperature of the melting point of the PAS orhigher, so that the polymer is melted. The thus-melted PAS iscontinuously extruded in the form of a sheet through a slit die such asa T-die, followed by its cooling and solidfying on a casting roll.

In this invention, the temperature, T of this casting roll is controlledto give a temperature in a range of 120°-190° C., depending on thethickness of the resultant sheet, namely, a temperature in a rangesatisfying the following equation (II):

    120≦T≦190-0.02t                              (II)

wherein t means a thickness (μm) of the sheet, to cool and crystallizethe sheet at one stage.

The sheet is more difficult to cool on the casting roll as it isthicker. It is hence necessary to control the temperature of the castingroll corresponding to the thickness of the sheet.

If the temperature of the casting roll is lower than the lower limit(120° C.) of the above equation, the sheet is substantially quenched toform an amorphous sheet. It is hence only possible to obtain a sheetinferior in mechanical properties. It is therefore difficult to providea sheet having a degree of crystallization of at least 5%. In addition,under such low-temperature conditions, crystallization does not veryproceed even when the residence time of the sheet on the casting roll iselongated. Further, the low-crystallized sheet is poor in separationproperty from the casting roll. It is hence difficult to obtain a sheethaving good planarity.

However, the separation property at low temperature itself is relativelyimproved if a ceramic is used as a material for the casting roll surfaceor a fluorine-containing release agent or the like is applied on thecasting roll. However, since the PAS sheet is characterized by highsusceptibility to elongation when it is in the amorphous state at atemperature not lower than the glass transition point, Tg of the PAS butnot higher than the lower limit of the above temperature range becauseno crystallization of the PAS sheet substantially proceeds, it isimpossible to obtain smooth separation property.

On the contrary, any temperatures of the casting roll exceeding theupper limit (about 190° C.) of the above equation (II) will result in asheet deteriorated in flex resistance. This is believed to be attributedto the fact that the temperature of the PAS, which leads to the maximumcrystallization rate, is about 190° C. and the crystallization in aregion beyond this temperature results in formation of largespherulites. In addition, it is assumed that crystal lamellae formingthe spherulites also become thicker and their crystal size becomeslarger as the temperature is higher, so that the tie chains linking thecrystal lamellae together also become a little. It is thereforeconsidered that the flex resistance is deteriorated because the bondingforce between crystal lamellae, and the interspherulite bonding forcebecome weak as has been described above. A preferred upper-limittemperature viewed from the point of flex resistance is about 175° C.,although it varies depending on the thickness of the sheet.

Viewed from the point of film-forming stability, it is possible to forma film up to a temperature at which crystallization becomes free fromoccurrence on the casting roll, i.e., about 240° C., although thecrystallization speed becomes slow when the temperature of the castingroll is higher than 190° C. However, the sheet formed in such ahigh-temperature region cannot be a sheet good in flex resistance fromthe reasons as described above.

The residence time of the melt-extruded sheet on the casting roll isgenerally 0.1-5 minutes, although it varies depending on the temperatureof the casting roll and the range of the melt crystallizationtemperature, Tc₂.

In order to cause the melt-extruded PAS sheet to closely adhere on thecasting roll, it is preferred to use a static-electricity applyingprocess. When using the static-electricity applying process incombination, it is possible to make a sheet more smooth.

When the crystallized PAS sheet obtained in the manner described aboveis subjected to an additional heat treatment at an elevated temperatureof 200°-280° C. for 0.1-180 minutes, a sheet having not only excellentplanarity and smoothness but also a still higher modulus of elasticitycan be obtained. The thus-obtained sheet is excellent in dimensionalstability. Below the lower limit of this temperature range, the degreeof crystallization may remain somewhat low and the modulus of elasticitymay not be increase substantially. In contrast, above the upper limit ofthis temperature range, the fusion of the PAS takes place and theplanarity and smoothness are deteriorated. Further, if the heating timeis shorter than the lower limit of the above range, effects of the heattreatment cannot be brought about fully. On the other hand, any undulylong heating time is not economical from the process consideration.

Production process of low-degree of crystallization sheet

A PAS sheet having a degree of crystallization controlled as low asabout 5-15% is superior in bending processability to conventionalcrystallized sheets. Therefore, even when the PAS sheet is subjected toa forming and processing by bending at room temperature (forming at atemperature of about 23° C. without heating), whitening and breaks atbent portions do not take place.

In the case of a low-degree of crystallization sheet as thick as 150 μmor more in particular, this phenomenon is remarkable compared tohigh-degree of crystallization sheets having the same thickness.

Upon the production of such a low-degree of crystallization PAS sheet,the range of its producing conditions is significantly limited. Itsproduction depends on the crystallization speed of PAS's own, i.e., itsmelt crystallization temperature, Tc₂ and moreover on the temperature ofa casting roll and the residence time of the PAS on the casting roll. Inthe case where sheets are formed industrially, it is important tocontrol the temperature of a casting roll and the residence time thereonin particular.

This respect will be described by examples.

FIG. 2 diagrammatically shows a relationship between the temperature ofa casting roll and the degree of crystallization when poly(p-phenylenesulfide) has been crystallized from a molten state on the casting rollto give a sheet thickness of 200 μm, wherein A and B indicate a casewhere the residence time on the casting roll is 90 seconds and a casewhere the residence time is 50 seconds, respectively. In the case of Ain FIG. 2, when the temperature of the casting roll is 128°C., itsdegree of crystallization is 3.4%, while the degree of crystallizationincreases to 22% when the temperature of the casting roll rises to 135°C. by 7° C. Therefore, in order to control the degree of crystallizationto a range of 5-15% in this case, the temperature of the casting rollmust be controlled within a range of 4° C. as 130°-134° C. This meansthat the temperature of the casting roll must be controlled verycarefully in the case where sheets ar produced industrially.

Further, B in FIG. 2 indicates a case where the residence time has beenmade short as 50 seconds. The shorter residence time indicates atendency to further limit the temperature range of the casting roll whencontrolling the sheet to a low degree of crystallization.

Similarly, FIG. 3 diagrammatically shows a relationship between thetemperature of a casting roll and the degree of crystallization whenpoly(p-phenylene sulfide) has been crystallized from a molten state onthe casting roll. D on the graph indicates a case where the thickness ofthe sheet is 200 μm, while C designates a case where the thickness ofthe sheet is 400 μm. The residence time on the casting roll is 90seconds in each case. The difference in heat quantity for cooling fromthe molten state becomes greater per area of a sheet as the sheet isthicker. It is hence necessary to lower the temperature of the castingroll relatively. The controlling range of the temperature tends tonarrow though it is a little.

In order to produce such a low-degree of crystallization PAS sheet, itis preferred to form a sheet by using a PAS having a meltcrystallization temperature, Tc₂ of 170°-220° C., and controlling thetemperature of the casting roll and the residence time on the castingroll respectively to 120°-160° C. and a range of 5-300 seconds.

Production conditions of oriented crystallized sheet

Besides, it is possible to provide an oriented sheet by using ahigh-viscosity PAS having a melt viscosity as high as at least 5,000poises, preferably 7,000 poises, controlling the delivery rate from aT-die and the take-up rate of a sheet and taking up at a relativelylarge drawdown ratio (draft ratio) upon melt extrusion and casting. Itis also possible to render the sheet 0.7 or lower in terms of thebelow-described degree of orientation. This sheet can be thined withease compared to a case where a low-viscosity PAS is used. The orientedcrystallized sheet thus obtained has further improved flex resistanceand mechanical properties such as yield strength and breaking strength.

A great feature of the sheet obtained by orienting and crystallizing onthe casting roll is that it is good in dimensional stability in spite ofthe oriented sheet. Such behavior is believed to be attributed to thefact that the stretched degree of amorphous chains is low, and thecrystalline size is relatively even and fine particulate crystals liableto melt are little. Such a structure is manifested by crystallizing amelt at an elevated temperature under molecular orientation. Thisprocess is preferred from the process economy because it does notrequire any high temperatures compared to such conventional processes asa sheet is stretched near at its glass transition point and thethus-stretched sheet is subjected to a heat treatment while maintainingits length constant to crystallize it. In addition, in the case of arelatively low orientation, its dimensional stability is furtherimproved and its strength and elongation in the drafting direction arealso great.

In order to obtain such an oriented crystallized sheet, it is necessaryto melt-extrude a PAS and then stretch the resulting sheet at apredetermined draft ratio or higher, thereby flow-orienting the sheetand at the same time cooling and crystallizing it. Specifically, it isnecessary to use a high-viscosity PAS having a melt viscosity not lowerthan a certain value, preferably, at least 7,000 poises as measured at310° C. and a share rate of 200 sec⁻¹. In the conventionally-known lowviscosity PAS, if a sheet thereof is flow-oriented, its relaxation rateis great and relaxation of orientation occurs. It is hence difficult tocrystallize it in an oriented state. More preferably, a PAS having sucha high melt viscosity is a resin in which a partially branched structurehas been introduced by using, as a monomer, a trihaloganated benzene inan amount of at least 0.05 mol % but at most 5 mol % in addition to adihalogenated benzene to increase its melt viscosity. Although the meltviscosity is preferably higher, any melt viscosities exceeding 25,000poises are accompanied by difficulties in melt extrusion.

When extruding the high-viscosity PAS as described above through a T-dieinto a sheet-like form, the temperature of the resin is preferably in arange of 290°-360° C. Although a lower temperature is preferred as atemperature of the resin in order to restrain the relaxation oforientation to efficiently orient and crystallize the sheet, such atemperature makes it difficult for the resin to flow in the extruder anddie. The resin extruded through the T-die is taken off by a castingroll. The take-off rate is made greater than the delivery rate of theresin (this ratio is referred to as "draft ratio"), thereby impartingflow orientation to molecular chains. At this time, it is morepreferable that the distance between the tip of the T-die and thecasting roll is shorter. Namely, there are effects shortening the timeof the process and enlarging the temperature gradient. However, itsdistance is generally set to about 5-30 mm because of the limitation asto apparatus.

The temperature of the casting roll is preferably at least 120° C.because the sheet requires to be crystallized on the roll. Thetemperature at which the maximum crystallization speed is imparted tothe poly(p-phenylene sulfide) resin is nearely 190° C. The sheet ishence crystallized faster as the temperature of the roll is nearer to190° C. Therefore, when the temperature of the roll becomes atemperature higher than 190° C., particularly, not lower than 200° C.,the crystallization also tends to become slow. Since the molten resin iscooled by the casting roll, the temperature of the resin is higher thanthat of the roll in an initial stage at which the resin has first comeinto contact with the roll. In addition, a sheet crystallized at anelevated temperature tends to be relatively inferior in flex resistanceto the sheet crystallized on a low-temperature casting roll, probably,in the cause of the formation of coarse spherulites. Such a sheet ishence not preferred. Therefore, the temperature of the casting roll ispreferably in a range of 120°-190° C. in general. Incidentally, it ispreferable that the draft ratio is generally at least 5, morepreferably, at least 10 in order to obtain an oriented crystallizedsheet, though it greatly depends on the melt viscosity of a resin to beused. The higher the draft ratio, the higher the orientation. However,its upper limit is about 5,000 in order to conduct stable take-up. As atake-up tension, at least 2.5 g/mm² or more is preferred.

Removing method of solvent-extracted low-molecular weight materials

When attempting to obtain a sheet of a low oligomer content in thisinvention, it is possible to produce a PAS sheet containingsolvent-extracted low-molecular weight materials such as oligomers insmaller amounts by using, as a PAS useful as a raw material for a sheet,a polymer treated in advance by melt extruding a PAS by a ventedextruder while drawing a vacuum from a vent zone through a vent port.

As the vented extruder, may be used either single-screw extruder andtwin-screw extruder. In order to reduce occurrence of color developmentof PAS and unmolten resin, and increase in melt viscosity, it ispreferred to hard chrome plate on the portions of the vented extruder,which come into contact with a molten resin, for example, the inner wallof a cylinder and the surface of a screw or to coat with a metal alloysuch as cobalt-chrome-boron on their surfaces, thereby covering themwith materials free of elemental iron as much as possible.

A PAS is generally heated to 310°-390° C. or so in the vented extruderinto a liquid state. It is considered that solvent extractedlow-molecular weight materials are removed from the molten resin bydrawing a vacuum from the extruder by means of a vacuum pump or the likethrough a vent port so as to reduce the pressure of a vent zone to atleast 400 mmHg or lower, preferably 100 mmHg or lower.

Accordingly, when a sheet is produce from a PAS obtained bymelt-extruding PAS powder as a raw material by a vented extruder whiledrawing a vacuum from a vent zone through a vent port in accordance withthe above-described process, a PAS sheet in which materials extracted byextraction with xylene is reduced to 0.5 wt. % or less and which hencecontains solvent-extracted low-molecular weight materials in smalleramounts can be obtained.

PAS Sheet

The PAS sheet according to this invention is excellent in planarity andsmoothness and has the following physical properties (physicalproperties before and after heat treatment):

(a) the surface roughness, Ra of at least one side of the sheet is 0.09μm or less;

(b) the degree of crystallization of the sheet is at least 5%; and

(c) the number of flexings to break, Y of the sheet satisfies thefollowing equation (I):

    log Y≧7.11-2.34log t                                (I)

wherein t means a thickness (μm) of the sheet.

The PAS sheet according to this invention is a formed product having athickness of, generally, 5 mm or less, preferably, from 10 μm to 2 mm,more preferably, from 20 μm to 600 μm.

The PAS sheet of this invention is superior in planarity and smoothnessto conventionally-known PAS sheets.

Described in regard to planarity, a PAS sheet obtained by a heattreatment method featuring contact of an amorphous sheet to a solidsurface such as a heating roll contains different spots correspondingrespectively to areas contacted or stuck to the solid and those floatedfrom the solid due to thermal expansion. In contrast, the PAS sheetaccording to this invention contains no distortion or warpage over theentire surface thereof, and has good planarity and smoothness, becauseit is obtained by cooling and crystallizing the sheet-like productmelt-extruded at one stage on a casting roll immediately without formingan amorphous sheet.

Regarding smoothness, the PAS sheet of this invention has suitablesurface roughness and small coefficient of dynamic friction on bothsurfaces thereof and has excellent utility. In particular, the surfaceroughness, Ra of the surface brought into contact with the casting rollis 0.09 μm or less, preferably 0.06 μm or less, more preferably 0.02 μmor less. It is hence extremely small compared with those of conventionalsheets.

The PAS sheet according to this invention is a crystallized sheet havinga degree of crystallization of at least 5%. A PAS sheet having a degreeof crystallization lower than 5% is insufficient in heat resistance.Such a sheet becomes extremely soft like a starch syrop in a temperaturerange exceeding the glass transition point of the PAS and is inferior inheat resistance, and is hence not practical. However, it may bepreferred to choose a suitable range of the degrees of crystallizationwithin ranges of the degrees of crystallization not lower than 5%depending on each intended end use because a PAS sheet having a lowerdegree of crystallization tends to exhibit better flex resistance.

With respect to mechanical properties, the PAS sheet of this inventionis excellent in various properties such as, not to speak of flexresistance, yield strength, breaking strength, elongation at break andtensile modulus. The sheet is hence very practical.

From the viewpoint of flex resistance, the PAS sheet of this inventionhas excellent flex resistance as demonstrated by its number of flexingsto break, Y satisfying the following equation (I):

    log Y≧7.11-2.34log t                                (I)

wherein t means a thickness (μm) of the sheet.

In particular, the oriented crystallized PAS sheet obtained by using ahigh-viscosity PAS and taking off at a high draft ratio can be providedas a thin film with ease and exhibits high flex resistance.

In addition, the PAS sheet according to this invention has goodmechanical properties as demonstrated by its yield strength of at least6 kg/mm², breaking strength of at least 4 kg/mm², elongation at break ofat least 10% and tensile modulus of at least 280 kg/mm² at 23° C.

These mechanical properties can be improved further by using ahigh-viscosity PAS having a melt viscosity of at least 10,000 poises andtaking off at a relatively great draft ratio upon casting, therebyforming an oriented crystallized sheet.

Furthermore, when a PAS treated in advance by melt-extruding by a ventedextruder while drawing a vacuum from a vent zone through a vent port isused as a raw PAS, a PAS sheet in which materials extracted byextraction with xylene is reduced to 0.5 wt. % or less and which hencecontains solvent-extracted low-molecular weight materials in smalleramounts is formed.

Even when the PAS sheet according to this invention is bent for itsprocessing or is set under tension or is subjected to drawing as invacuum forming or pressure forming, the sheet is sufficiently resistantto breakage.

Application Fields

PAS sheets according to this invention have a surface roughness, Ra ofat most 0.09 μm on its one sides and are hence extremely smooth.Therefore, they can be suitably used, for example, as base films formagnetic recording materials such as base films for floppy disks, inwhich planarity and smoothness are required, by roughening the othersides to facilitate separation and sliding.

Besides, the PAS sheets of this invention can be used in a wide varietyof application fields in which heat resistance, planarity, smoothness,flex resistance and the like are required, for example, in the field ofelectronic and electrical engineering as capacitor films, flexibleprinted circuit boards, chip carriers and TAB (tapes for automatedbonding) and in some cases, in the field of mechanical engineering assliding members like bushings which are each formed of an iron plate anda filler-added film bonded to the iron plate.

A PAS sheet in which materials extracted by extraction with xylene isreduced to 0.5 wt. % or less and which hence contains solvent-extractedlow-molecular weight materials in smaller amounts is suitably used inapplications in which mechanical properties such as flex resistance,heat resistance and Fleon resistance and at the same time, an extremelylow oligomer content (low content of solvent-extracted materials) arerequired, for example, as sheets for insulating the motors ofcoolant-compressors.

ADVANTAGES OF THE INVENTION

According to the present invention, there is economically provided a PASsheet comprising a PAS as a raw material and having excellentdimensional stability to heat, planarity, smoothness and mechanicalproperties such as flex resistance.

According to this invention, there is also provided a PAS sheet havingthe above-mentioned physical properties and containing solvent-extractedlow-molecular weight materials in smaller amounts.

EMBODIMENTS OF THE INVENTION

The present invention will hereinafter be described specifically by thefollowing Examples and Comparative Examples. It should however be bornein mind that this invention is not limited to the following Examplesonly.

Measurements of physical properties:

The following methods were followed for the measurement ofcharacteristic data of PAS and PAS sheets in this invention.

Melt viscosity

The melt viscosity of each PAS was measured at 310° C. and a shear rateof 200 sec⁻¹.

Melt crystallization temperature

The melt crystallization temperature, Tc₂ of each PAS was determined byreading an exothermic peak temperature of crystallization, whichappeared upon the measurement by a DSC at a cooling rate of 10° C./minafter the PAS is heated from 23° C. to 380° C. at a rate of 10° C./minand then held for 3 minutes at 380° C., from a graph.

Surface roughness

Each surface roughness, Ra (μm) was measured in accordance with JISB-0601, using a surface roughness meter ("SURFCOM 550A", trade name;manufactured by Tokyo Seimitsu Co., Ltd.).

Coefficient of dynamic friction

Each coefficient of dynamic friction was measured in accordance withASTM D 1894, using a "Friction Meter, Model TR" manufactured by ToyoSeiki Seisakusho, Ltd.

Degree of crystallization

A density gradient tube was formed using a zinc chloride-water system.From specific gravity (ρ) measured at 23° C., crystalline density (ρc)and amorphous density (ρa), the weight-average degree of crystallization(Xc) was determined in accordance with the following equation:

    Xc=(ρc/ρ){(ρ-ρa)/(ρc-ρa)}

Incidentally, ρc of the poly(phenylene sulfide) used in the presentExamples was 1.4300 from the data of literature [ρc=1.43 in Europeanpolymer Journal, Vol. 7, 1127(1971)] and ρa was 1.3125 as a measuredaverage value of samples which were identified as an amorphous formamong various samples prepared by quenching.

Breaking strength, elongation at break, tensile modulus and yieldstrength

Using "TENSILON" (trade name) manufactured by Toyo-Baldwin Company,sample sheets punched out by a No. 5 dumbbell were measured at 23° C.and 200° C. respectively in accordance with ASTM D-638. The samplelength, width and stretching rate were set at 33 mm, 6 mm and 50 mm/minrespectively. The breaking strength and elongation at break weredetermined from a strain-stress curve, while the tensile modulus wasdetermined from the initial strain zone. Further, a yield stress isdefined as the yield strength.

Degree of orientation

A strip of 1 mm wide was cut out of a sheet, which had been obtained byexactly arranging samples in their take-up direction and laminating themso as to give a thickness of at least 4 mm, in parallel with the take updirection. The strip specimen thus cut out was set on a fibrous specimencarrier attached to a K-ray diffractometer manufactured by Rigaku DenkiK.K. in such a manner that X-rays struck on the specimen in parallelwith the direction of the width of 1 mm and at a right angle to thethickness-wise direction of the sheet laminated to give the thickness ofat least 4 mm (namely, in such a manner that the X-rays struck on thespecimen sheet in a direction perpendicular to an edge face thereof).

The specimen was set perpendicularly and 2 scanning was conducted in theequatorial direction to determine a diffraction peak intensity of the(200) plane (I.sub.φ=0). The specimen was then inclined by 30° from theperpendicular direction and 2 scanning was similarly conducted todetermine a diffraction peak intensity of the (200) plane (I.sub.φ=30).

The degree of orientation was determined by I.sub.φ=30 /I.sub.φ=0.

Incidentally, when a PAS sheet is not oriented, its degree oforientation is a value of 0.7 or greater.

Flex resistance--The number of flexings to break

A strip of 100 mm long and 15 mm wide was cut out of each sample to bemeasured. Using an MIT flexural fatigue resistance testing machinemanufactured by Toyo Seiki Seisakusho, Ltd., the strip sample was set ata chuck interval of 55 mm in accordance with JIS -8115 and was flexedfrom side to side under a load of 1.25 kg at a flexure angle of 135degree and a flexure rate of 175 times/min. The number of flexings untilthe sample sheet was broken was then determined as an index of flexresistance.

Contents of materials extracted with xylene

Square pieces of 1 cm×1 cm were cut out of each PAS sheet. Ten grams ofthe pieces were exactly weighed and placed in a flask equipped with acondenser. Further, 100 cc of a commercially-available xylene (specialgrade) was placed in the flask. The flask was put in an oil bath kept atabout 155° C. and solvent-extracted low-molecular weight materials wereextracted from the sample pieces while boiling xylene (the boiling pointof xylene: about 140° C.). After the extraction was continuouslyconducted for 72 hours, xylene was cooled to room temperature. Aresulting xylene solution was then pour into a weighing bottle. Theflask in which the sample pieces remained was washed 3 times with 100 ccin total of xylene. The liquid after the washing was added to theweighing bottle.

The weighing bottle was then heated to about 85° C. and at the sametime, xylene was evaporated to a constant weight under slightly reducedpressure, thereby removing xylene. The residue was then weighed todefine its weight as the weight of materials extracted with xylene. Theweight percentage of the extracted materials by the xylene extractionwas found by dividing the weight of the materials extracted with xyleneby 100 and multiplying the quotient by 100.

EXAMPLE 1

Substantially linear poly(p-phenylene sulfide) having a melt viscosityof 7,300 poises (as measured at 310° C. and a shear rate of 200 sec⁻¹)and a melt crystallization temperature, Tc₂ of 172° C. (an exothermicpeak temperature of crystallization which appeared upon the measurementby a DSC at a cooling rate of 10° C./min after the pAS is heated from23° C. to 380° C. at a rate of 10° C./min and then held for 3 minutes at380° C.) was melt-extruded into pellets.

The pellets thus obtained were extruded into a sheet-like form through aT-die which was fitted to an extruder having a barrel diameter of 35 mmand an L/D ratio of 28 and defined a lip having a clearance of 0.55 mmand a width of 250 mm. The melt temperature of the resin was 310° C.,and the delivery rate was 3.0 kg/hour. The distance between the tip ofthe T-die and the upper portion of a casting roll was adjusted to about10 mm. The surface temperature of the casting roll was controlled at155° C. The casting roll had a diameter of 300 mm.

The take-up rate was controlled so that the sheet thus wound had athickness of 190 μm. The take-up rate was 0.85 m/min.

The thus obtained sheet had a density of 1.341 g/cm³ at 23° C. Thedegree of crystallization found from this value was 25.9%. The surfaceroughness, Ra of the sheet were 0.050 μm and 0.130 μm on the sidebrought into contact with the casting roll and on the opposite sidethereto, respectively. The sheet had a coefficient of dynamic frictionof 0.3 on the side brought into contact with the casting roll. Withrespect to flex resistance, its number of flexings to break wasmeasured. It was found to be 320 times.

Further, the sheet was subjected to a heat treatment for 10 minutes at260° C. by heated air in a Geer oven to facilitate its crystallization.The sheet thus heat-treated had surface roughness, Ra of 0.060 μm and0.140 μm on the side kept into contact with the casting roll and on theopposite side thereto, respectively. Its degree of crystallizationincreased to 33.1%. The heat-treated sheet had a coefficient of dynamicfriction of 0.3 on the side brought into contact with the casting roll.With respect to flex resistance, its number of flexings to break wasmeasured. It was found to be 110 times. Furthermore, the heat-treatedsheet had a yield strength of 9 kg/mm², breaking strength of 6 kg/mm²,elongation at break of 40% and tensile modulus of 330 kg/mm².

COMPARATIVE EXAMPLE 1 AND 2

Sheets were separately produced by using the same raw pellets andapparatus as those employed in Example 1 under the same conditions as inExample 1 except that the temperature of the casting roll was changed.The measurement results as to the relationships between the surfacetemperature of the casting roll and the separation property and degreeof crystallization of the thus-obtained sheets are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                        Temperature of    Separation                                                                              Degree of                                         casting roll      property  crystallization                                   (°C.)      of sheet  of sheet (%)                                      ______________________________________                                        Comp.    80           Good        0                                           Ex. 1                                                                         Comp.   105           Inferior  <10                                           Ex. 2                                                                         ______________________________________                                    

The sheet of Comparative Example 1 had good surface roughness, Ra of0.010 μm on both sides, but was substantially amorphous. Its breakingstrength was 6 kg/mm² at room temperature, but became extremely weak asabout 0.1 kg/mm² at 120° C. Therefore, it deformed under slight externalforce and was hence in a state difficult to maintain its form. The sheetwas subjected to a heat treatment for 10 minutes at 260° C. by heatedair in a Geer oven to facilitate its crystallization. Its degree ofcrystallization was increased to about 33%. However, it was impossibleto conduct an even heat treatment over the entire sheet. Therefore,warpage and surface irregularity were too significant to measure itsmechanical properties.

The sheet of Comparative Example 2 was inferior in separation propertyfrom the casting roll. No smooth sheet was hence obtained. Therefore,local irregularity also resided in its degree of crystallization. Allwas 10% or lower. In addition, it was infeasible to measure its surfaceroughness and its mechanical properties after the heat treatment due tothe warpage and thickness irregularity of the sheet, which were causedby the inferiority in separation from the casting roll.

EXAMPLE 2: (APPLICATION EXAMPLE OF NUCLEATING AGENT)

Pellets were produced from a system composed of 100 parts by weight ofsubstantially linear poly(p-phenylene sulfide) having a melt viscosityof 6,800 poises (as measured at 310° C. and a shear rate of 200 sec⁻¹)and a melt crystallization temperature, Tc₂ of 204° C. and 1.0 parts byweight of carbon black ("Mitsubishi Carbon MA-100", trade name) as anucleating agent.

Using the pellets thus obtained, a crystallized sheet was produced bythe same apparatus as in Example 1 at a melt temperature of 310° C., adelivery rate of 3.0 kg/hour and a casting roll temperature of 160° C.The take-up rate was controlled so that the sheet thus wound had athickness of 160 μm. The take-up rate was 1.0 m/min.

Upon the take-up of the sheet, it separated from a casting roll withextreme smoothness. The sheet thus obtained had a degree ofcrystallization of 27.0% and was very smooth as demonstrated by itssurface roughness, Ra of 0.010 μm on the side brought into contact withthe casting roll. The surface roughness, Ra of the opposite side theretowas 0.040 μm.

The state of formation of spherulites was observed through a scanningelectron microscope. Spherulites were not formed but an extremely finewave-like structure was formed on the surface.

Further, the sheet was subjected to a heat treatment for 10 minutes at260° C. by heated air in a Geer oven to facilitate its crystallization.The sheet thus heat-treated had surface roughness, Ra of 0.010 μm and0.040 μm on the side brought into contact with the casting roll and onthe opposite side thereto, respectively.

Measurement results of physical properties and others are collectivelygiven in Table 2.

EXAMPLE 3

Using the same poly(p-phenylene sulfide) as that used in Example 2except for the omission of the nucleating agent, a sheet of 160 μm thickwas obtained under the same conditions as in Example 2.

Upon the take-up of &he sheet, it separated from a casting roll withextreme smoothness. The sheet thus obtained had a degree ofcrystallization of 26.1% and surface roughness, Ra of 0.040 μm and 0.110μm on the side brought into contact with the casting roll and on theopposite side thereto, respectively.

Measurement results of physical properties and others are collectivelygiven in Table 2.

EXAMPLE 4: (APPLICATION EXAMPLE OF STATIC-ELECTRICITY APPLYING PROCESS

The same raw pellets as those used in Example 1 were melt-extruded bythe same apparatus as that in Example 1 at a melt temperature of 310° C.and a delivery rate of 3.0 kg/hour. The surface temperature of a castingroll was 185° C. At this time, a tungsten-made wire (pinning wire) of0.15 mm across was stretched in parallel with the axis of the roll at aposition separated by 5 mm in the radial direction of the roll from thepoint of the roll, at which the molten resin extruded contacted. About5.0 kV of direct current voltage was applied between the wire and theroll to cast the sheet under application of static electricity.

The thus-obtained sheet had a thickness of 160 μm and the take up ratewas about 1.0 m/min. The degree of crystallization of the sheet was27.5%. The surface roughness, Ra of the sheet were 0.020 μm and 0.100 μmon the side brought into contact with the casting roll and on thepinning wire side, respectively.

Further, the sheet was subjected to a heat treatment for 10 minutes at260° C. by heated air in a Geer oven. The sheet thus heat-treated had adegree of crystallization of 33.1% and surface roughness, Ra of 0.030 μmand 0.090 μm on the casting roll side and on the pinning wire side,respectively.

Measurement results of physical properties and others are collectivelygiven in Table 2.

Comparative Example 3 EXAMPLE 5

Using the same raw pellets as those employed in Example 4, a sheet of160 μm thick was obtained under the same conditions as in Example 4except for the omission of the static-electricity application to thepinning wire.

The sheet thus obtained had a degree of crystallization of 28.4% andsurface roughness, Ra of 0.060 μm and 0.150 μm on the side brought intocontact with the casting roll and on the opposite side thereto,respectively.

Further, the sheet was subjected to a heat treatment for 10 minutes at260° C. by heated air in a Geer oven. The sheet thus heat-treated had adegree of crystallization of 35.0% and surface roughness, Ra of 0.060 μmand 0.160 μm on the side brought into contact with the casting roll andon the opposite side thereto, respectively.

Measurement results of physical properties and others are collectivelygiven in Table 2.

COMPARATIVE EXAMPLE 3

Substantially linear poly(p-phenylene sulfide) having a melt viscosityof 870 poises and a melt crystallization temperature, Tc₂ of 253° C. wasmelt-extruded into pellets.

A sheet was produced from the thus-obtained pellets by means of the sameapparatus as that employed in Example 1 using a static-electricityapplying device under the same conditions as in Example 4. The surfacetemperature of the casting roll was 170° C. The crystallized sheet thusobtained had a thickness of 260 μm.

The sheet had a degree of crystallization of 34 0%. Besides, the surfaceroughness, Ra of the sheet were 0.010 μm and 0.007 μm on the sidebrought into contact with the surface of the casting roll and on thepinning wire side, respectively.

Further, the sheet was subjected to a heat treatment for 10 minutes at260° C. by heated air in a Geer oven to facilitate its crystallization.The sheet thus heat-treated had a degree of crystallization of 38.6%.Besides, its surface roughness, Ra were 0.009 μm and 0.010 μm on theside brought into contact with the casting roll and on the pinning wireside, respectively. Its degree of crystallization increased to 33.1%.

With respect to flex resistance, its number of flexings to break wasmeasured. It was found to be twice for the sheet before the heattreatment and once for the sheet after the heat treatment. Therefore,the sheet was inferior in flex resistance and was brittle, and can hencenot be subjected to bend processing or the like.

Measurement results of physical properties and others are collectivelygiven in Table 2.

EXAMPLE 6

Substantially linear poly(p-phenylene sulfide) having a melt viscosityof 9,400 poises (as measured at 310° C. and a shear rate of 200 sec⁻¹)and a melt crystallization temperature, Tc₂ of 179° C. was melt-extrudedinto pellets.

The pellets thus obtained were melt-extruded by the same apparatus as inExample 4 at a melt temperature of 310° C. and a delivery rate of 2.1kg/hour. The surface temperature of a casting roll was 150° C. At thistime, about 5.0 kV of direct current voltage was applied between apinning wire and the roll to cast the sheet under application of staticelectricity. The take-up rate was about 0.57 m/min. The thus-obtainedsheet had a thickness of about 200 μm.

Its number of flexings to break was measured. It was found to be 370times. The sheet was subjected to a heat treatment for 10 minutes at260° C. in a Geer oven. The number of flexings to break of the sheetthus heat-treated was 140 times.

EXAMPLE 7

A sheet was obtained in the same manner as in Example 6 except that thesurface temperature of the casting roll was changed from 150° C. to 175°C.

The number of flexings to break of the thus-obtained sheet was measured.It was found to be 140 times. The sheet was subjected to a heattreatment for 10 minutes at 260° C. in a Geer oven. The number offlexings to break of the sheet thus heat-treated was 105 times.

Measurement results of physical properties and others are collectivelygiven in Table 2.

Incidentally, results in Example 15, which will be describedsubsequently, are also shown collectively in Table 2.

                                      TABLE 2                                     __________________________________________________________________________                          Comp.                                                                             Comp.                Comp.                                            Ex. 1                                                                             Ex. 1                                                                             Ex. 2                                                                              Ex. 2                                                                             Ex. 3                                                                             Ex. 4                                                                             Ex. 5                                                                             Ex. 3                                                                             Ex. 6                                                                             Ex.                                                                               Ex.                __________________________________________________________________________                                                               15                 PPS                                                                           Melt viscosity, η* (poises)                                                                 7,300                                                                             7,300                                                                             7,300                                                                              6,800                                                                             7,300                                                                             7,300                                                                             7,300                                                                             870 9,400                                                                             9,400                                                                             3.100              Melt crystallization temperature,                                                               172 172 172  204 204 172 172 253 179 179 205                Tc.sub.2 (°C.)                                                         Nucleating agent (carbon black) (phr)                                                           --  --  --   1   --  --  --  --  --  --  --                 Processing conditions                                                         Melt temperature (°C.)                                                                   310 310 310  310 310 310 310 310 310 310 310                Delivery rate (kg/hour)                                                                         3.0 3.0 3.0  3.0 3.0 3.0 3.0 3.2 2.1 2.1 3.0                Surface temperature of casting                                                                  155 80  105  160 160 155 155 170 150 175 150                roll (°C.)                                                             Applied static electricity (kV)                                                                 --  --  --   --  --  5.0 --  5.0 5.0 5.0 5.0                Take-up rate (m/min)                                                                            0.85                                                                              0.87                                                                              0.87 1.0 1.0 1.0 1.0 0.66                                                                              0.57                                                                              0.57                                                                              1.35                Physical properties of sheet                                                 Separation property from casting roll                                                           Good                                                                              Good                                                                              Inferior                                                                           Good                                                                              Good                                                                              Good                                                                              Good                                                                              Good                                                                              Good                                                                              Good                                                                              Good               Thickness of sheet (μm)                                                                      190 190 190  160 160 160 160 260 200 200 120                Density (g/cm.sup.3)                                                                            1.341                                                                             --  --   --  --  --                  1.341              Degree of crystallization (%)                                                                   25.9                                                                              0   <10  27.0                                                                              26.1                                                                              27.5                                                                              28.4                                                                              34.0                                                                              --  --  27.6               Surface roughness, Ra (μm)                                                 Casting roll side 0.050                                                                             0.010                                                                             --   0.010                                                                             0.045                                                                             0.020                                                                             0.060                                                                             0.010                                                                             --  --  0.045              Opposite side     0.130                                                                             0.010                                                                             --   0.040                                                                             0.110                                                                             0.100                                                                             0.150                                                                             0.007                                                                             --  --  0.110              __________________________________________________________________________                           Comp.                                                                             Comp.               Comp.                                             Ex. 1                                                                             Ex. 1                                                                             Ex. 2                                                                             Ex. 2                                                                             Ex. 3                                                                             Ex. 4                                                                             Ex. 5                                                                             Ex. 3                                                                             Ex. 6                                                                             Ex.                                                                               Ex.                __________________________________________________________________________                                                               15                 Physical properties of heat-treated sheet                                     Heat treatment (260° C./10 min)                                                           Con-                                                                              Not Not Con-                                                                              Not Con-                                                                              Not Con-                                                                              Con-                                                                              Con-                                                                              Con-                                  ducted                                                                            con-                                                                              con-                                                                              ducted                                                                            con-                                                                              ducted                                                                            con-                                                                              ducted                                                                            ducted                                                                            ducted                                                                            ducted                                    ducted                                                                            ducted  ducted  ducted                             Degree of crystallization (%)                                                                    33.1                                                                              --  --  35.9                                                                              --  33.1                                                                              35  38.6                                                                              --  --  30                 Surface roughness, Ra (μm)                                                 Casting roll side  0.060                                                                             --  --  0.010                                                                             --  0.030                                                                             0.060                                                                             0.009                                                                             --  --  0.055              Opposite side      0.140                                                                             --  --  0.040                                                                             --  0.090                                                                             0.160                                                                             0.010                                                                             --  --  0.130              Yield strength (kg/mm.sup.2)                                                                     9   --  --  9   --  9   --  10  --  --  9                  Breaking strength (kg/mm.sup.2)                                                                  6   --  --  6   --  6   --  6   --  --  7                  Elongation at break (%)                                                                          40  --  --  32  --  40  --  10  --  --  30                 Tensile modulus (kg/mm.sup.2)                                                                    330 --  --  350 --  330 --  370 --  --  320                Degree of orientation                                                                            0.96                                                                              --  --  0.95                                                                              --  0.95                                                                              --  0.97                                                                              --  --  0.97               Number of flexings to break                                                   Before heat treatment                                                                            320 440 --  230 250 260 --  2   370 140 370                After heat treatment (260° C./10 min)                                                     110 --  --  160 --  100 --  1   140 105 180                Coefficient of dynamic friction                                               Before heat treatment                                                                            0.3 --  --  0.4 --  0.3 --  0.3 --  --  0.3                After heat treatment (260° C./10 min)                                                     0.3 --  --  0.4 --  0.3 --  0.3 --  --  0.3                Y value found from log Y = 7.11-                                                                 60  60  60  90  90  90  90  29  53  53  176                2.34 log t (times)                                                            __________________________________________________________________________

EXAMPLES 8-13

Pellets were produced from high-viscosity poly(p-phenylene sulfide),which had been obtained by polymerizing a system composed of 100 partsby weight of dichlorobenzene and 0.2 part by weight of trichlorobenzeneand had a melt viscosity of 14,000 poises (as measured at 310° C. and ashear rate of 200 sec⁻¹) and a melt crystallization temperature, Tc₂ of198° C. Portions of the pellets thus obtained were separatelymelt-extruded by means of the same apparatus as that employed in Example1 and each of the extrudates was crystallized on a casting roll, therebyproducing sheets. At this time, temperatures of each melt to be extrudedand a die portion were controlled to 315° C. and 320° C. respectively.

The delivery rate was 2.1 kg/hour. Applied voltage of astatic-electricity applying device was 4.0 kV and the surfacetemperature of the casting roll was 155° C. Take-up rates of sheets tobe formed were respectively changed to produce sheets having theircorresponding thicknesses as shown in Table 3. All of the thus-obtainedsheets were good in separating from the casting roll and excellent inappearance.

However, casting was conducted by reducing the delivery rate to about1.0 kg/hour and controlling the take-up rate in Example 12. Besides, thedelivery rate was reduced to about 0.5 kg/hour to take up the sheet inExample 13. Other conditions were the same as those in Example 8.

                  TABLE 3                                                         ______________________________________                                              Take-up rate                                                                              Thickness of                                                                              Degree of                                       Ex.   (m/min)     sheet (μm)                                                                             crystallization (%)                             ______________________________________                                         8    0.28        400         26.5                                             9    0.57        200         27.5                                            10    1.13        100         28.4                                            11    1.89         60         28.4                                            12    2.69         20         29.3                                            13    3.37         8          29.3                                            ______________________________________                                    

The sheet obtained in Example 9 had surface roughness, Ra of 0.010 μmand 0.025 μm on the side brought into contact with the casting roll andon the pinning wire side, respectively. The sheet had a yield strengthof 8 kg/mm², a breaking strength of 6 kg/mm², an elongation at break of44% and a tensile modulus of 300 kg/mm².

Further, the sheet was subjected to a heat treatment for 10 minutes at260° C. by heated air in a Geer oven to facilitate its crystallization.The sheet thus heat-treated had a degree of crystallization of 33.1% andsurface roughness, Ra of 0.024 μm and 0.035 μm on the casting roll sideand on the pinning wire side, respectively. The sheet had a yieldstrength of 9 kg/mm², a breaking strength of 6 kg/mm², an elongation atbreak of 31% and a tensile modulus of 310 kg/mm². Furthermore, the sheetof Example 13 was subjected to a heat treatment for 10 minutes at 260°C. by heated air in a Geer oven to facilitate its crystallization. Atthis time, the sheet was free in both machine and transverse directions.The sheet after the heat treatment shrunk by 2.5% in length and 0% inwidth, respectively, based on the length and width of the sheet beforethe heat treatment. The heat-treated sheet had a degree ofcrystallization of 33.1%. The thus-obtained sheet, which had beensubjected to the heat treatment for 10 minutes at 260° C. to facilitateits crystallization, was subjected further to a heat treatment for 10minutes at 255° C. in a manner that the sheet was free in both machineand transverse directions. Percent changes in dimensions of theheat-treated sheet were 0% in both machine and transverse directions. Onthe other hand, an amorphous sheet was produced by a method known per sein the art using the same resin as that in Example 13. The sheet wasstretched 3.5 times in the machine direction and 3.5 times in thetransverse direction by sequential biaxial stretching. The thus-obtainedfilm was subjected to a heat treatment for 10 minutes at 260° C. whilemaintaining its length constant. The film had a thickness of 15 μm. Thebiaxially-stretched film was subjected further to a heat treatment for10 minutes at 255° C. in a manner that the sheet was free in bothmachine and transverse directions. Percent shrinkages of theheat-treated film were 4% and 6% in its machine and transversedirections, respectively.

As described above, the crystallized sheet obtained in Example 13 wassmall in percent heat shrinkage and hence excellent in dimensionalstability to heat. The degree of crystalline orientation of theresulting sheet was 0.47 as determined by striking X-rays on the sheetin a direction perpendicular to an edge face thereof. The sheet washence found to be oriented to a great extent. The numbers of flexings tobreak of the crystallized sheet obtained in Example 13 were 200,000times and 100,000 times before and after the heat treatment,respectively, indicating that the sheet had high reflex resistance.

The data of the characteristics and properties of the sheets obtained inthese Examples, processing conditions and others are shown collectivelyin Table 4.

                                      TABLE 4                                     __________________________________________________________________________                         Ex. 8 Ex. 9 Ex. 10                                                                              Ex. 11                                                                              Ex. 12                                                                              Ex. 13                     __________________________________________________________________________    PPS                                                                           Melt viscosity, η* (poises)                                                                    14,000                                                                              14,000                                                                              14,000                                                                              14,000                                                                              14,000                                                                              14,000                     Melt crystallization temperature, Tc.sub.2 (°C.)                                            198   198   198   198   198   198                        Nucleating agent (carbon black) (phr)                                                              --    --    --    --    --    --                         Processing conditions                                                         Melt temperature (°C.)                                                                      315   315   315   315   315   315                        Delivery rate (kg/hour)                                                                            2.1   2.1   2.1   2.1   1.0   0.5                        Surface temperature of casting roll (°C.)                                                   155   155   155   155   155   155                        Applied static electricity (kV)                                                                    4.0   4.0   4.0   4.0   4.0   4.0                        Take-up rate (m/min) 0.28  0.57  1.13  1.89  2.69  3.37                       Physical properties of sheet                                                  Separation property from casting roll                                                              Good  Good  Good  Good  Good  Good                       Thickness of sheet (μm)                                                                         400   200   100   60    20    8                          Density (g/cm.sup.3) --    --    --    --    --    --                         Degree of crystallization (%)                                                                      26.5  27.5  28.4  28.4  29.3  29.3                       Surface roughness, Ra (μm)                                                 Casting roll side    0.012 0.010 0.010 0.009 0.008 0.008                      Opposite side        0.030 0.025 0.020 0.013 0.010 0.010                      Physical properties of heat-treated sheet                                     Heat treatment (260° C./10 min)                                                             Conducted                                                                           Conducted                                                                           Conducted                                                                           Conducted                                                                           Conducted                                                                           Conducted                  Degree of crystallization (%)                                                                      32.1  33.1  33.1  34.0  34.0  33.1                       Surface roughness Ra (μm)                                                  Casting roll side    0.020 0.024 0.020 0.015 0.012 0.010                      Opposite side        0.035 0.035 0.030 0.020 0.015 0.013                      Yield strength (kg/mm.sup.2)                                                                       9     9     9     8     8     8                          Breaking strength (kg/mm.sup.2)                                                                    6     6     7     7     15    20                         Elongation at break (%)                                                                            30    31    50    60    120   150                        Tensile modulus (kg/mm.sup.2)                                                                      300   310   310   320   330   340                        Degree of orientation                                                                              0.96  0.93  0.87  0.79  0.61  0.47                       Number of flexings to break                                                   Before heat treatment                                                                              50    160   1,100 8,000 80,000                                                                              200,000                    After heat treatment (260° C./10 min)                                                       35    80    800   7,000 35,000                                                                              100,000                    Coefficient of dynamic friction                                               Before heat treatment                                                                              0.3   0.3   0.3   0.4   0.4   0.4                        After heat treatment (260° C./10 min)                                                       0.3   0.3   0.3   0.4   0.4   0.4                        Y value found from log Y = 7.11-2.34 log t                                                         11    53    269   890   11,630                                                                              99,260                     (times)                                                                       __________________________________________________________________________

EXAMPLE 14

Substantially linear poly(p-phenylene sulfide) having a melt viscosityof 9,400 poises and a melt crystallization temperature, Tc₂ of 179° C.was melt-extruded into pellets.

The pellets thus obtained were extruded into a sheet-like form through aT-die which was fitted to an extruder having a barrel diameter of 35 mmand defined a lip having a width of 250 mm. The melt temperature of theresin was 310° C., and the delivery rate was 2.1 kg/hour. The surfacetemperature of the casting roll was 132° C. At this time, atungsten-made wire (pinning wire) of 0.15 mm across was stretched inparallel with the axis of the roll at a position separated by 5 mm inthe radial direction of the roll from the point of the roll, at whichthe molten resin extruded contacted. About 4.5 kV of direct currentvoltage was applied between the wire and the roll to cast the sheetunder application of static electricity. The take-up rate of the sheetwas about 0.58 m/min.

The thus-obtained sheet had a thickness of 200 μm and the degree ofcrystallization of the sheet was 6%. The surface roughness, Ra of thesheet were 0.018 μm and 0.110 μm on the side brought into contact withthe casting roll and on the pinning wire side, respectively. The sheetwill be designated as "Sheet A".

With respect to the flex resistance of the Sheet A, its number offlexings to break was measured. It was found to be 380 times.

Further, the Sheet A was subjected to a heat treatment on a ceramic rollcontrolled at 240° C. The residence time of the sheet on the ceramicroll was about 1 minute. The sheet thus heat-treated had a degree ofcrystallization of 24%. In addition, its number of flexings to break was140 times. The heat-treated sheet will be designated as "Sheet B".

On the other hand, an amorphous sheet of 200 μm thick was produced bychanging the temperature of the casting roll to 50° C. and using thesame extruding conditions, pinning conditions and take-up rate as inExample 14. The degree of crystallization of the thus-produced sheet waszero. Its number of flexings to break was 420 times. The amorphous sheetwill be designated as "Sheet C".

With a view toward observing the high-temperature resistance of theSheets A, B and C, the sheets were separately heated by a "ThermoMechanical Analyzer (TMA) 40" manufactured by Mettler Instrument AG at aheating rate of 2° C./min under a slight load of 1.7 g/mm². Theelongation or shrinkage behavior of the sheets where they were heated inthis manner is illustrated in FIG. 1. In FIG. 1, lines (1), (2) and (3)show the elongation or shrinkage behavior of Sheets A, B and C,respectively.

It is understood from FIG. 1 that the amorphous sheet C undergoes agreat deformation when the sheet reaches a temperature level beyond theglass transition point (about 90° C.) of the sheet, thereby leading toits break due to the elongation thereof [line (3)].

On the other hand, although Sheet A having a degree of crystallizationof 6% exhibits some elongation due to the expansion of its amorphousportions and the like in a temperature range beyond the glass transitionpoints of the sheet, a great deformation leading to its break does nottake place in a high-temperature range up to at least 250° C. [line(1)].

Further, Sheet B having a degree of crystallization of 24% exhibits thebehavior as depicted by the line (2) on FIG. 1. The behavior exhibitedis substantially the same elongation behavior as that of the Sheet A.Since the Sheet B is high in degree of crystallization compared to theSheet A, the deformation as to elongation in the temperature rangebeyond the glass transition point is less than that of the Sheet A.

COMPARATIVE EXAMPLE A

A heat treatment apparatus constructed of a ceramic roll having asurface roughness, Ra of 0.063 μm and a diameter of 150 mm, arubber-made pinch roll, etc. was provided. At this time, the gaugepressure and the pinch pressure of the linear pressure were respectively3.0 kg/cm² and 1.2 kg/cm. Moreover, the temperature of the ceramic rollwas controlled at 155° C. On the other hand, the surface temperature ofthe rubber roll was about 100° C.

After the amorphous sheet obtained in Comparative Example 1 and having athickness of 190 μm was fed along and in contact with the surface of thepinch roll to preheat it for 10 seconds, the sheet was introduced intothe pinching point. After passing through the pinch point, the sheet wastransferred onto the ceramic roll on which the sheet was subjected to aheat treatment and was hence crystallized. The residence time of thesheet on the ceramic roll was about 30 seconds. On the other hand, theperipheral speed of the surface of the ceramic roll was about 0.3 m/min.

Under those conditions, a crystallized sheet was produced bylinearly-pressurizing the amorphous sheet with the pinch roll and thencrystallizing it. The thus-obtained sheet was wound up on a take-uproll.

The sheet thus obtained had surface roughness, Ra of 0.150 μm and 0.170μm on the ceramic roll side and on the pinch roll side, respectively.The sheet had a degree of crystallization of 20%, a breaking strength of5.2 kg/mm², an elongation at break of 80% and a Young's modulus of 350kg/mm². Its number of flexings to break was 130 times. Moreover, thecoefficient of dynamic friction of the crystallized sheet as to thepinch roll side was 0.3 as measured against another sheet of the samekind as the crystallized sheet.

EXAMPLE 15

Substantially linear poly(p-phenylene sulfide) having a melt viscosityof 3,100 poises and a melt crystallization temperature, Tc₂ of 205° C.was melt-extruded into pellets.

The pellets thus obtained were extruded into a sheet-like form through aT-die which was fitted to an extruder having a barrel diameter of 35 mmand an L/D ratio of 28 and defined a lip having a clearance of 0.55 mmand a width of 250 mm. The melt temperature of the resin was 310° C. andthe delivery rate was 3.0 kg/hour. The distance between the tip of theT-die and the upper portion of a casting roll was adjusted to about 10mm. The surface temperature of the casting roll was controlled at 150°C. The casting roll had a diameter of 300 mm.

The take-up rate was controlled so that the sheet thus wound had athickness of 120 μm. The take-up rate was 1.35 m/min.

The thus-obtained sheet had a density of 1.343 g/cm³ at 23° C. Thedegree of crystallization found from this value was 27.6%. The surfaceroughness, Ra of the sheet were 0.045 μm and 0.110 μm on the sidebrought into contact with the casting roll and on the opposite sidethereto, respectively. The sheet had a coefficient of dynamic frictionof 0.3 on the side brought into contact with the casting roll withrespect to flex resistance, its number of flexings to break wasmeasured. It was found to be 370 times.

Further, the sheet was subjected to a heat treatment for 10 minutes at260° C. by heated air in a Geer oven to facilitate its crystallization.The sheet thus heat-treated had surface roughness, Ra of 0.055 μm and0.130 μm on the side kept into contact with the casting roll and on theopposite side thereto, respectively. Its degree of crystallizationincreased to 30%. Its degree of orientation was 0.97. Moreover, theheat-treated sheet had a coefficient of dynamic friction of 0.3 on theside brought into contact with the casting roll.

With respect to flex resistance, its number of flexings to break wasmeasured. It was found to be 180 times.

Furthermore, the heat-treated sheet had a yield strength of 9 kg/mm²,breaking strength of 7 kg/mm², elongation at break of 30% and tensilemodulus of 320 kg/mm².

EXAMPLE 16: (USE OF VENTED EXTRUDER)

As a PAS, was used powder of substantially linear poly(p-phenylenesulfide) having a melt viscosity, η^(*) of 9,400 poises and a meltcrystallization temperature, Tc₂ of 179° C. Moreover, as a ventedextruder, was used a twin-screw extruder "BT-30" manufactured by PlasticKogaku K.K. [wherein the surface of the cylinder part was coated with"H-503" (Ni-Co-Cr-Si-B alloy; product of Hitachi Metals, Ltd.), and thescrews were subjected to hard chrome plating]. A vacuum pump having acold trap was attached to a vent port of the extruder.

The powder of the poly(p-phenylene sulfide) was melt-extruded by thetwin-screw extruder at the melt temperature of the polymer, i.e., 320°C. into strings. The strings were cooled with water into pellets. Thetwin-screw extruder was made vacuous by drawing a vacuum with the vacuumpump attached to a vent zone through the vent port to removesolvent-extracted low-molecular weight materials from the polymer. Thedelivery rate of the melt was about 10 kg/hour. The degree of vacuum bythe vacuum-drawing was read from a pressure gauge attached near to thevent zone. It read about -72 cmHg (about 40 mmHg).

The pellets thus obtained were melt-extruded into a sheet-like formthrough a T-die which was fitted to a single screw extruder having abarrel diameter of 35 mm and an L/D ratio of 28 and defined a lip havinga width of 25 cm and a lip clearance of 0.5 mm. The melt temperature ofthe polymer was 310° C. and the delivery rate was 2.5 kg/hour. Thedistance between the tip of the T-die and a casting roll was adjusted toabout 10 mm. The surface temperature of the casting roll was controlledat 130° C. The casting roll had a diameter of 300 mm.

The take up rate was controlled to 0.68 m/min so that the sheet thuswound had a thickness of 200 μm. Incidentally, a tungsten-made wire(pinning wire) of 0.15 mm across was stretched in parallel with the axisof the casting roll, and static casting was conducted while applyingabout 5 kV of direct current voltage between the wire and the roll.

The thus-obtained sheet had a density of 1.325 g/cm³ at 23° C. Thedegree of crystallization found from this value was 12%. The surfaceroughness, Ra of the sheet were 0.022 μm and 0.049 μm on the sidebrought into contact with the casting roll and on the opposite sidethereto, respectively. The sheet had a coefficient of dynamic frictionof 0.3 on the side brought into contact with the casting roll. Withrespect to flex resistance, its number of flexings to break wasmeasured. It was found to be 370 times.

Further, the sheet was subjected to a heat treatment for 10 minutes at260° C. by heated air in a Geer oven to facilitate its crystallization.The heat-treated sheet had a degree of crystallization of 28% and adegree of orientation of 0.96. Its surface roughness, Ra were 0.030 μmand a 0.055 μm on the side kept into contact with the casting roll andon the opposite side thereto, respectively. Moreover, the heat-treatedsheet had a coefficient of dynamic friction of 0.3 on the side broughtinto contact with the casting roll. Its number of flexings to break was120 times. The heat-treated sheet had a yield strength of g kg/mm²,breaking strength of 7 kg/mm², elongation at break of 40% and tensilemodulus of 330 kg/mm².

The amount of materials extracted with xylene from this sheet was 0.27wt. % of the sheet sample. By the way, this value is an average value ofmeasurements obtained by conducting the above-describedxylene-extraction process three times as to sheet samples from the samesheet.

According to the process like this, it is possible to obtain a sheethaving an extremely-low oligomer content.

EXAMPLE 17: (USE OF VENTED EXTRUDER)

Using the same vented twin-screw extruder as that employed in Example16, pellets were produced from powder of substantially linearpoly(p-phenylene sulfide) having a melt viscosity, η^(*) of 5,900 poisesand a melt crystallization temperature, Tc₂ of 200° C. The pelletizationconditions as to extrusion temperature and delivery rate were alsosubstantially the same. The degree of vacuum by the vacuum-drawing wasabout -70 cmHg (about 60 mmHg) from the indication of a pressure gauge.

The pellets thus obtained were melt-extruded into a sheet-like formunder the same conditions as in Example 16. The sheet was thencrystallized on a casting roll to obtain a sheet of 200 μm thick.

The amount of materials extracted with xylene from the sheet, which wasdetermined in the same manner as in Example 16, was 0.43 wt. %.

The thus-obtained sheet had a density of 1.320 g/cm³ at 23° C. Thedegree of crystallization found from this value was 7%. The surfaceroughness, Ra of the sheet were 0.018 μm and 0.045 μm on the sidebrought into contact with the casting roll and on the opposite sidethereto, respectively. The sheet had a coefficient of dynamic frictionof 0.3 on the side brought into contact with the casting roll. Withrespect to flex resistance, its number of flexings to break wasmeasured. It was found to be 350 times.

Further, the sheet was subjected to a heat treatment for 10 minutes at260° C. by heated air in a Geer oven to facilitate its crystallization.The heat-treated sheet had a degree of crystallization of 27% and adegree of orientation of 0.98. Its surface roughness, Ra were 0.026 μmand 0.052 μm on the side kept into contact with the casting roll and onthe opposite side thereto, respectively. Moreover, the heat-treatedsheet had a coefficient of dynamic friction of 0.3 on the side broughtinto contact with the casting roll. Its number of flexings to break was105 times. The heat-treated sheet had a yield strength of 9 kg/mm²,breaking strength of 7 kg/mm², elongation at break of 30% and tensilemodulus of 350 kg/mm².

EXAMPLE 18: (SHEET FOR INSULATING MOTOR OF COOLANT-COMPRESSORBend-processing

A sample of 85×25 mm in size was cut out of the crystallized sheet(heat-treated sheet; degree of crystallization: 28%) obtained in Example16. The sample was heated to 125° C. and bend for processing in aU-shaped form (at 180°). This bend-processing was conducted 5 times. Nocracks occurred on the outside of the bent part in all the processings.On the contrary, when the bend-processing was performed at roomtemperature, cracks were recognized in the proportion of 3 times to 5times.

When the sheet-like formed product obtained by the bend-processing wasused as an sheet-like formed product for insulating a motor of acoolant-compressor, the compressor was able to use for a long period oftime without trouble though the motor was a heat build-up type.

EXAMPLE 19: (BEND-PROCESSING OF LOW-DEGREE OF CRYSTALLIZATION SHEET ATROOM TEMPERATURE)

The sheet produced in Example 17 and having a degree of crystallizationof 7% and a length of 10 cm was slit into a strip of 85 mm wide. Thestrip was caused to pass between a pair of rotating metal rolls, whichwere controlled at room temperature (23° C.), while bending it atpositions advanced inside by 3 mm from both ends into a U-shape, wherebythe strip was bent and its shape was fixed.

The clearance between the pair of the metal rolls was about 0.5 mm. Itwas finely adjusted manually so that sufficient bending and fixing wereconducted. The sheet thus obtained was bended and fixed to a sufficientextent. Moreover, no whitening and break were recognized at the bentparts. The sheet hence had sufficient practical utility.

EXAMPLES 20-21

Using the same resin as that employed in Example 8, which had a meltviscosity of 14,000 poises, casting was conducted by extruding the resinat a delivery rate of 2.0 kg/hour under the same extruding conditions asin Example 8 and controlling the take-up rate. The take-up rate was 1.62m/min and the thickness of the resulting sheet was 50 μm. The sheet hada degree of crystallization of 23% and a degree of orientation of 0.75(Example 20).

On the other hand, using the same resin as that employed in Example 1,which had a melt viscosity of 7,300 poises, a sheet of 50 μm thick wasproduced at a delivery rate of 2.0 kg/hour and a take-up rate of 2.16m/min under the same conditions as described above. The thus-obtainedsheet had a degree of crystallization of 22% and a degree of orientationof 0.97, which indicated substantially no orientation (Example 21).

The drawdown ratios (draft ratios) of these sheet are both 11 becausethe clearance of the extruder die lip is 0.55 mm.

On the other hand, in order to determine the winding tensions of thesheets in the case when the draft ratio was 11 at a melt temperature of310° C., each of their resins was extruded at a melt temperature of 310°C. by a Capillograph through a nozzle of 1.0 mm in diameter and 10 mm inlength. At this time, the winding tension of a strand extruded wasmeasured at a draft ratio of 11.

In the case of the resin employed in Example 20, the winding tensionunder the above conditions was 8 g and there was hence a tension of 10g/mm² to the sectional area of the nozzle. In the case of the resin usedin Example 21 on the other hand, the winding tension was 1 g and therewas hence a tension of 1.3 g/mm² to the sectional area of the nozzle.

With respect to these sheets, the percent heat shrinkages in bothmachine and transverse directions were 1.0/0 (MD/TD) in the sheet ofExample 20 and 0.5/0 (MD/TD) in the sheet of Example 21. They were hencegood in each sheet.

The determination of the winding tension to what extent also depends onthe properties of a resin to be used and processing conditions. A sheetobtained under conditions of a high winding tension is great in degreeof crystalline orientation from its edge face. This makes its elongationat break high in the machine direction (MD). In this invention, thepreferred winding tension is at least 2.5 g/mm².

What is claimed is:
 1. In a poly(arylene sulfide) sheet excellent inplanarity and smoothness, said sheet being formed of a poly(arylenesulfide) having a melt viscosity, η^(*) of 1,000-25,000 poises asmeasured at 310° C. and a shear rate of 200 sec⁻¹, and a meltcrystallization temperature, Tc₂ of 170°-240° C. wherein Tc₂ is anexothermic peak temperature of crystallization which appears upon themeasurement by a differential scanning calorimeter at a cooling rate of10° C./min after the polymer is heated from 23° C. to 380° C. at a rateof 10° C./min and then held for 3 minutes at 380° C., the improvementwherein:(a) the surface roughness, Ra of at least one side of the sheetis 0.09 μm or less; (b) the degree of crystallization of the sheet is atleast 5%; and (c) the number of flexings to break, Y of the sheetsatisfies the following equation (I):

    log Y≧7.11-2.34log t                                (I)

wherein t means a thickness (μm) of the sheet.
 2. The poly(arylenesulfide) sheet as claimed in claim 1, wherein the sheet containsmaterials extracted by extraction with xylene in an amount of 0.5 wt. %or less of the whole weight before extraction.
 3. A sheet for insulatingthe motor of a coolant-compressor, which comprises the poly(arylenesulfide) sheet as claimed in claim
 2. 4. The poly(arylene sulfide) sheetas claimed in claim 1, which has a melt viscosity, η^(*) of at least8,000 poises as measured at 310° C. and a shear rate of 200 sec⁻¹ andhas been uniaxially oriented.